The present invention relates to a bit sliced decimal adding/subtracting unit of the type in which n1-digit decimal adder/subtracters are used for n-digit decimal addition and subtraction.
Generally, the expression of decimal numbers is categorized into a pack format and a zone format. In the pack format, one digit consists of 4 bits. The addition and subtraction in the pack format, therefore, could be realized by using merely a single 1-digit decimal adder/subtracter. Actually, however, a multi-digit (e.g. n-digit) decimal adder/subtracter consisting of a plurality of 1-digit decimal adder/subtracters is employed in order to reduce the operating time since the number of digits of an operand is large.
In the zone format, one digit of the decimal number consists of 8 bits (one byte). The lower four bits of each byte are used for expressing a decimal number. The upper four bits of each byte are for designating zone data. Thus, the data format of the zone format is different from that of the pack format. For this reason, to apply the n-digit decimal adder/subtracters to the adding and subtracting of the decimal numbers of the zone type, the operand of the zone type must be changed into the pack type operand. This data format changing is accompanied by complicated procedural steps.